<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
	</body>
	<script type="text/javascript">
		/*
		 	1. Boolean()
		 	2. !/!!
		*/
		var a = "";
		var b = 0;
		var c = null;
		var d =undefined;
		
		var ar = !!a; 
		var br = !!b; 
		var cr= !!c;
		var dr = !!d;
		
		console.log(ar,typeof ar);
		console.log(br,typeof br);
		console.log(cr,typeof cr);
		console.log(dr,typeof dr);
		
		
		//引用数据类型
		//只看真假值
		var arr =[1,2,3];
		var arrR = !![1,2,3];
		console.log(arrR,typeof arrR)
		
	</script>
</html>
